Broadly viewed, this program of research is directed toward a further understanding of those factors that influence the social behavior of animals. Especially emphasized are the neural and endocrine activities that may both determine and result from social interaction. The program is based upon recognition of the fact that the internal milieu of certain animals is highly responsive to changes in the social environment. Conversely, changes in the internal state of the organism can lead to significant alterations in social behavior. Consideration of these reciprocal relationships forms the basis for the studies with which we are immediately concerned. Successful reproduction in the ring dove depends upon a complex division of labor. The male and female must coordinate their behavior during courtship, nest construction, incubation of the eggs, and care of the offspring. The efficiency and success of their reproductive efforts appear to be heavily influenced by a number of contributory factors. It is the purpose of this research program to determine the extent to which the physiological state of the pair, their reproductive experience, their familiarity with one another as individuals, their complementarity of styles, and their separate strategies as males and females affect the survival, health, and vigor of their offspring.